Abstract: A hybrid waveform and model-based image signal encoder and decoder are described. The image signal is waveform-encoded (11) and decoded (31) so as to approximate the waveform of the original input signal as well as possible after compression. In order to compensate its loss, the noise component of the signal (or, more generally, a signal component which gets lost by the waveform encoding) is model-based encoded (12,13) and separately transmitted or stored. In the decoder, the noise is regenerated (32-34) and added (36) to the waveform-decoded image signal. The invention is particularly applicable to compression of medical X-ray angiographic images where loss of noise leads a cardiologist or radiologist to believe that the image is distorted.

Abstract: System for transmitting n video programs simultaneously through a transmission channel having a predetermined bitrate, comprising in cascade a decoding assembly and an encoding assembly. The decoding assembly consists of n parallel decoding means provided in parallel for decoding the coded input signals corresponding to said programs, and the encoding assembly consists of n encoding means being in cascade with each of said decoding means and each comprising a quantizer having a variable step size and a variable length encoder. The system also comprises means for controlling the step sizes of said encoding means in dependence upon their respective output bitrates, and these control means are also provided for controlling the output bitrates of said encoding means in dependence upon complexity values associated to the coded input signals of each decoding means with respect to the joint complexity of the plurality of said coded signals.

Abstract: A method of transcoding coded video signals and a corresponding device for implementing this method are described. The device comprises decoding and encoding sub-assemblies (201, 202) and, within the encoding sub-assembly, quantizer (23) and bitrate controller. This bitrate controller comprise, before the quantizer (23), circuit for computing a local target value for encoding each sub-picture of the images to which video signals correspond and circuit for controlling the step size during the quantizing step.